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{{Short description|Functional segment of the large intestine}}
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{{Infobox Anatomy |
{{more citations needed|date=December 2018}}
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Name = {{PAGENAME}} |
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{{Infobox anatomy
Latin = canalis analis |
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| Name = Anal canal
GraySubject = 249 |
GrayPage = 1184 |
| Latin = canalis analis
Image = Gray1078.png |
| Greek =
| Image = File:Anorectum-en.svg
Caption = Coronal section of [[rectum]] and anal canal. |
| Caption = Anatomy of the anus and rectum
Image2 = Gray1079.png |
| Width =
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Caption2 = Coronal section through the anal canal. B. Cavity of [[urinary bladder]] V.D. [[Vas deferens|Ductus deferens]]. S.V. [[Seminal vesicle]]. R. Second part of [[rectum]]. A.C. Anal canal. L.A. [[Levator ani]]. I.S. [[Sphincter ani internus muscle|Sphincter ani internus]]. E.S. [[Sphincter ani externus muscle|Sphinear ani externus]]. |
System = |
| Image2 = Gray1079.png
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| Caption2 = Coronal section through the anal canal. B. Cavity of [[urinary bladder]] V.D. [[Vas deferens|Ductus deferens]]. S.V. [[Seminal vesicle]]. R. Second part of [[rectum]]. A.C. Anal canal. L.A. [[Levator ani]]. I.S. [[Internal anal sphincter|Sphincter ani internus]]. E.S. [[External anal sphincter|Sphincter ani externus]].
Artery = [[inferior rectal artery]] |
Vein = [[inferior rectal vein]] |
| Precursor = [[Hindgut]], [[proctodeum]]
Nerve = |
| System =
Lymph = [[superficial inguinal lymph node]] (below [[pectinate line]]) [[internal iliac lymph nodes]] (above line) |
| Artery = [[Superior rectal artery]] (above [[pectinate line]]) and [[inferior rectal artery]] (below line)
| Vein = [[Superior rectal vein]] (above pectinate line) and [[Inferior rectal vein]] (below line)
Precursor = [[hindgut]], [[proctodeum]] |
| Nerve = [[Autonomic nervous system|Autonomic]] [[inferior hypogastric plexus]] (above pectinate line) and [[Somatic nervous system|somatic]] [[inferior rectal nerves]] (below line)
MeshName = Anal+Canal |
| Lymph = [[Superficial inguinal lymph node]] (below pectinate line) and [[internal iliac lymph nodes]] (above line)
MeshNumber = A03.556.124.526.070 |
DorlandsPre = c_04 |
DorlandsSuf = 12208538 |
}}
}}
The '''anal canal''' is the part that connects the [[rectum]] to the [[anus]], located below the level of the [[pelvic diaphragm]].<ref name=Goldman2020>{{cite book |last1=Madoff |first1=Robert D. |last2=Melton-Meax |first2=Genevieve B. |editor1-last=Goldman |editor1-first=Lee |editor2-last=Schafer |editor2-first=Andrew I. |title=Goldman-Cecil Medicine |date=2020 |publisher=Elsevier |location=Philadelphia |isbn=978-0-323-55087-1 |page=933 |edition=26th |volume=1 |chapter-url=https://books.google.com/books?id=7pKqDwAAQBAJ&pg=PA933 |language=en |chapter=136. Diseases of the rectum and anus }}</ref> It is located within the [[anal triangle]] of the [[perineum]], between the right and left [[ischioanal fossa]]. As the final functional segment of the [[bowel]], it functions to regulate release of [[excrement]] by two muscular [[sphincter]] complexes. The anus is the aperture at the terminal portion of the anal canal.
The '''anal canal''' is the terminal part of the [[large intestine]].<ref>{{MeshName|Anal+Canal}}</ref>


==Structure==
It is situated between the [[rectum]] and [[anus]],<ref>{{DorlandsDict|two/000016124|anal canal}}</ref> below the level of the [[pelvic diaphragm]]. It lies in the [[anal triangle]] of [[perineum]] in between the right and left [[ischiorectal fossae]].
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In humans, the anal canal is approximately {{cvt|2.5 to 4|cm}} long, from the anorectal junction to the [[Human anus|anus]].<ref>{{Cite web|title=Anal canal|url=https://www.knowyourbody.net/anal-canal.html}}</ref><ref>{{MeSH name|Anal+Canal}}</ref><ref>{{Cite web|url=https://www.knowyourbody.net/anal-canal.html|title = Anal Canal - Location, Function and Pictures}}</ref> It is directed downwards and backwards. It is surrounded by inner involuntary and outer voluntary sphincters which keep the [[lumen (anatomy)|lumen]] closed in the form of an anteroposterior slit.


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The canal is differentiated from the rectum by a transition along the internal surface from [[endodermal]] to skin-like [[ectodermal]] tissue.
The anal canal is divided into three parts. The zona columnaris is the upper half of the canal and is lined by [[simple columnar epithelium]]. The lower half of the anal canal, below the [[pectinate line]], is divided into two zones separated by [[Hilton's white line]]. The two parts are the zona hemorrhagica and zona cutanea, lined by [[stratified squamous epithelium|stratified squamous non-keratinized]] and [[stratified squamous epithelium|stratified squamous keratinized]], respectively.


The anal canal is traditionally divided into two segments, upper and lower, separated by the [[pectinate line]] (also known as the dentate line):
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In humans it is approximately 2.5 to 4 cm long, extending from the anorectal junction to the [[anus]]. It is directed downwards and backwards. It is surrounded by inner involuntary and outer voluntary sphincters which keep the [[lumen (anatomy)|lumen]] closed in the form of an anteroposterior slit.


* upper zone (zona columnaris)
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It is differentiated from the rectum by the transition of the internal surface from [[endodermal]] to skinlike [[ectodermal]] tissue.
** mucosa is lined by [[simple columnar epithelium]]
** features longitudinal folds or elevations of tunica mucosa which are joined inferiorly by folds of [[mucous membrane]] known as [[anal valves]]
** supplied by the [[superior rectal artery]] (a branch of the [[inferior mesenteric artery]])
* lower zone
** divided into two smaller zones, separated by a white line known as the [[Intersphincteric groove|Hilton's line]]:
*** zona hemorrhagica - lined by [[stratified squamous epithelium|stratified squamous non-keratinized epithelium]]
*** zona cutanea - lined [[stratified squamous epithelium|stratified squamous keratinized epithelium]], which blends with the surrounding perianal skin
** supplied by the [[inferior rectal artery]] (a branch of the [[internal pudendal artery]])


The '''anal verge''' refers to the [[Anatomical terms of location#Proximal and distal|distal]] end of the anal canal, a transitional zone between the [[epithelium]] of the anal canal and the [[perianal skin]]. It should not be confused with the pectinate line between the upper and lower zones within the anal canal.
==Upper and Lower Divisions==
The anal canal is divided into two unequal sections, upper and lower.
* The upper 2/3 has longitudinal folds or elevations of tunica mucosa. Its mucosa is lined by [[simple columnar epithelium]]. Its lower ends are joined together by folds of mucus membrane called anal valves. The upper 2/3 of the anal canal is supplied by the [[superior rectal artery]] which is a branch of the [[inferior mesenteric artery]].


The '''[[anal gland]]''' secretes lymphal discharge and built-up [[feces|fecal matter]] from the [[large intestine|colon]] lining. In some animals this gland expungement can be done routinely every 24–36 months to prevent infection and [[fistula]] formation.
* The lower 1/3 of the anal canal is lined by [[stratified squamous epithelium]] that blends with the skin. The lower third of the anal canal is supplied by the [[inferior rectal artery]] which is a branch of the [[internal pudendal artery]].


===Relations===
A whitish line called [[Hilton's white line]] indicates the junction between keratinized stratified squamous epithelium and unkeratinized stratified squamous epithelium.
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*The [[ischioanal fossa]] are on each side of the anal canal.

==Surgical spaces related to the anal canal==
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*The [[ischiorectal fossa]] lies on each side of the anal canal.
*The [[perianal space]] surrounds the anal canal below the white line.
*The [[perianal space]] surrounds the anal canal below the white line.
*The submucous space of the canal lies above the white line between the mucous membrane and [[internal anal sphincter]].
*The submucous space of the canal lies above the white line between the mucous membrane and [[internal anal sphincter muscle]].

==Function==
The [[external anal sphincter]] muscle is the voluntary muscle that surrounds and adheres to the anus at the lower margin of the anal canal. This muscle is in a state of [[tetanic contraction|tonic contraction]], but during [[defecation]], it relaxes to allow the release of [[feces]].

Movement of the feces is also controlled by the involuntarily controlled internal anal sphincter, which is an extension of the circular muscle surrounding the anal canal. It relaxes to expel feces from the rectum and anal canal.


==Additional images==
==Additional images==
<gallery>
<gallery>
Image:Anorectum.gif |Anatomy of the anus and rectum
Image:Anorectum-en.svg |Anatomy of the anus and rectum
Image:Gray404.png|Left Levator ani from within.
Image:Gray404.png|Left levator ani from within
Image:Gray1080.png|The interior of the anal cami and lower part of the rectum.
Image:Gray1080.png|The interior of the anal canal and lower part of the rectum
Image:Gray1228.png|Median sagittal section of male pelvis.
Image:Gray1228.png|Median sagittal section of male pelvis
Image:Gray1230.png|Median sagittal section of female pelvis.
Image:Gray1230.png|Median sagittal section of female pelvis
</gallery>
</gallery>


==See also==
==See also==
{{Anatomy terms}}
* [[Anal columns]]
* [[Anal columns]]
* [[Anal sinuses]]
* [[Anal sinuses]]
* [[Anal valves]]
* [[Anal sex]]
* [[Pectinate line]]
* [[anus]]


==References==
==References==
{{reflist}}
{{Reflist}}


==External links==
==External links==
* {{NormanAnatomy|pelvis}}
* {{NormanAnatomy|Pelvis}}
* {{SUNYAnatomyFigs|44|05|00}} - "The rectum and anal canal in the male pelvis."
* {{SUNYAnatomyFigs|44|05|00}}&nbsp;— "The rectum and anal canal in the male pelvis"
* {{eMedicineDictionary|Anal+canal}}


{{Digestive system}}
{{Digestive tract}}
{{Authority control}}


[[Category:Digestive system]]
[[Category:Digestive system]]
[[Category:Anus|Canal]]

{{digestive-stub}}

[[ar:قناة الشرج]]
[[dv:ފުރަގަސް ފަރާތު މަގު]]
[[fr:Canal anal]]
[[it:Canale anale]]
[[pt:Canal anal]]
[[ru:Заднепроходной канал человека]]
[[fi:Peräaukkokanava]]

Latest revision as of 20:09, 8 November 2024

Anal canal
Anatomy of the anus and rectum
Coronal section through the anal canal. B. Cavity of urinary bladder V.D. Ductus deferens. S.V. Seminal vesicle. R. Second part of rectum. A.C. Anal canal. L.A. Levator ani. I.S. Sphincter ani internus. E.S. Sphincter ani externus.
Details
PrecursorHindgut, proctodeum
ArterySuperior rectal artery (above pectinate line) and inferior rectal artery (below line)
VeinSuperior rectal vein (above pectinate line) and Inferior rectal vein (below line)
NerveAutonomic inferior hypogastric plexus (above pectinate line) and somatic inferior rectal nerves (below line)
LymphSuperficial inguinal lymph node (below pectinate line) and internal iliac lymph nodes (above line)
Identifiers
Latincanalis analis
MeSHD001003
TA98A05.7.05.001
TA23009
FMA15703
Anatomical terminology

The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm.[1] It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional segment of the bowel, it functions to regulate release of excrement by two muscular sphincter complexes. The anus is the aperture at the terminal portion of the anal canal.

Structure

[edit]

In humans, the anal canal is approximately 2.5 to 4 cm (0.98 to 1.57 in) long, from the anorectal junction to the anus.[2][3][4] It is directed downwards and backwards. It is surrounded by inner involuntary and outer voluntary sphincters which keep the lumen closed in the form of an anteroposterior slit.

The canal is differentiated from the rectum by a transition along the internal surface from endodermal to skin-like ectodermal tissue.

The anal canal is traditionally divided into two segments, upper and lower, separated by the pectinate line (also known as the dentate line):

The anal verge refers to the distal end of the anal canal, a transitional zone between the epithelium of the anal canal and the perianal skin. It should not be confused with the pectinate line between the upper and lower zones within the anal canal.

The anal gland secretes lymphal discharge and built-up fecal matter from the colon lining. In some animals this gland expungement can be done routinely every 24–36 months to prevent infection and fistula formation.

Relations

[edit]

Function

[edit]

The external anal sphincter muscle is the voluntary muscle that surrounds and adheres to the anus at the lower margin of the anal canal. This muscle is in a state of tonic contraction, but during defecation, it relaxes to allow the release of feces.

Movement of the feces is also controlled by the involuntarily controlled internal anal sphincter, which is an extension of the circular muscle surrounding the anal canal. It relaxes to expel feces from the rectum and anal canal.

Additional images

[edit]
  • Anatomy of the anus and rectum
    Anatomy of the anus and rectum
  • Left levator ani from within
    Left levator ani from within
  • The interior of the anal canal and lower part of the rectum
    The interior of the anal canal and lower part of the rectum
  • Median sagittal section of male pelvis
    Median sagittal section of male pelvis
  • Median sagittal section of female pelvis
    Median sagittal section of female pelvis

See also

[edit]
This article uses anatomical terminology.

References

[edit]
  1. ^ Madoff, Robert D.; Melton-Meax, Genevieve B. (2020). "136. Diseases of the rectum and anus". In Goldman, Lee; Schafer, Andrew I. (eds.). Goldman-Cecil Medicine. Vol. 1 (26th ed.). Philadelphia: Elsevier. p. 933. ISBN 978-0-323-55087-1.
  2. ^ "Anal canal".
  3. ^ Anal+Canal at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
  4. ^ "Anal Canal - Location, Function and Pictures".
[edit]
  • Pelvis at The Anatomy Lesson by Wesley Norman (Georgetown University)
  • Anatomy figure: 44:05-00 at Human Anatomy Online, SUNY Downstate Medical Center — "The rectum and anal canal in the male pelvis"
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